Production of low sulfur formcoke



Jan. 14, 1964 J. D. BATCHELOR EI'AL 3,117,913

PRODUCTION OF LOW SULFUR FORMCOKE Filed Sept. 13, 1960 s Shets-Sheet 1 FLUIDIZED GAS LTC TAR BRIQUET l2 PREPARATION SHOCK HEATING HEAT AND HOLDING TAR AND GAS HYDROGEN CALCINING AND HEAT DESULFURIZING COOLANT COOLING H PRODUCT DESULFURIZED FORMCOKE FIG. I

INVENTORS. JAMES D. BATCHELOR GEORGE P. CURRAN ROBERT J.FRBT$DRICH EVERETT GORIN Jan. 14, 1964 J. D. BATCHELOR ETAL Filed Sept. 13, 1960 8 Sheets-Sheet 2 BRIQUETS HOTS 1 29 GASE AIR 21 BURNER FUEL GAS 20 1 2a z? SHOCK HEATING N AND HOLDING zone H32 GASES 1 a. TAR NET GAS RECOVERY TAR PRODUCTS COKED BRIQUETS FIG. 2.

JAMES D. BATCHELOR IN VEN TORS. GEORGE E CURRAN ROBERT J. FRAE DRICH EVERETT GORIN Jan. 14, 1964 J. D. BATCHELOR ETAL 7,

PRODUCTION OF LOW SULFUR FORMCOKE Filed Sept. 13, 1960 8 Sheets-Sheet 3 BRIQUETS l TARQ TAR PRODUCTS 44 RECOVERY GAS 42 58 59 so HEATER VESSEL 57 FOR HEAT CARRYING 0 MATERIAL 48 r40 r41 5L SHOCK HEATlNG AND HOLDING ZONE FLUIDIZING AND 55 3 FLUIDIZING eAs CARRYING GAS F Q1 E 45 STRIPPING L 60 GAS COKED BRIQUETS FIG. 3

INVENTORS.

JAMES D. BATCHELOR GEORGE P. CURRAN ROBERT J. FRIEDRICH EVERETT GORIN J 14, 1954 J. D. BATCHELOR ETAL 3,117,918

PRODUCTION OF LOW SULFUR FOkMCOKE Filed Sept. 15, 1960 a Sheets-Sheet 4 COKED smouers A HEAT 79 EXCHANGER 8 f5? 74 H s a REMOVAL DESULFURIZING AND 84 CALCINING 1 ZONE :l :1 1:: :l I: 1:: 1:1 :1

1: m c: :11: :1 cu:

cl I: as l: c! c: x: REGENERATIVE EIDDEIDEHIIIII CHECKERWORK 1:: l: D 1:: c: :1 :1

::| 1: I: I: :1 1: c: 1::

$5 86 {77 AIR HOT HYDROGEN-RICH 73 GAS 75 FUEL DESULFURIZED CALCINED BRIQUETS FIG. 4

Jan. 14, 1964 J. D. BATCHELOR ETAL 3,117,913

PRODUCTION OF LOW SULFUR FORMCOKE Filed Sept. 13, 1960 8 Sheets-Sheet 5 CQKED BRIQUETS 98 I09 H2 92 j 5 E Y NET I06 GAS ACCEPTOR REGENERATOR VESSEL DESULFURIZATION AND CALCINING ZONE no? I u COOLING zone IOI m FIG. 5

TOR

Jan. 14, 1964 J. D. BATCHELOR ETAL 7,

PRODUCTION OF Low SULFUR FORMC'OKE Filed Sept. 13, 1960 8 Sheets-Sheet 6 FROM SHOCKHEATING ZONE I20 LOCK l2 HOPPER I27 FIG. 6

TO CALCINING AND DESULFURIZING ZONE FROM CALCINING ZONE C A HEATED FUEL GAS I30 LOCK l3l HOPPER COLD PRODUCT Fl 7 INVEN TOR. JAMES D. BATCHELOR GEORGE P. CURRAN ROBERT J. FRAE DRIOU EVERETT GORIN Jan. 14, 1964 J. D. BATCHELOR ETAL PRODUCTION OF LOW SULFUR FORMCOKE 8 Sheets-Sheet 7 Filed Sept. 13, 1960 93 m 5; $25 6: Qz wzifi. v.85 Emma m; a Na zonfimE 555 o IN V EN TORS.

mEDGEm owxoo JAMES D. BATCHELOR GEORGE P. CURRAN ROBERT J. FRIEDRICH EVERETT GORIN H 200 FQDQOmE Jan. 14, 1964 J. D. BATCHELOR ETAL 3,117,918

PRODUCTION OF LOW SULFUR FORMCOKE 8 Sheets-Sheet 8 Filed Sept. 13, 1960 mmm homma QwNEDuJDmMQ FonoOmm E/Lr mzON OENEDuJDmMQ INVENTORS. JAMES D. BATCHELOR GEORGE P. CURRAN ROBERT J. FRBJiE DRICH EVERETT GORIN atet dice 913 ULFUR FQRM CUXL in, Va. an George P, 5. Eric: 7 Finsny iig This invention relates to a method for preparing lowsulfur formcoke of metallurgical grade from calling bituminous coal cont in r substantial quantities of sulfur. it particularly relates to an improvement in desulfurizing sulfur-containing coal-char agglomerates.

This application is a continuation-in-part of our copending applications Serial Number 853,742, filed November 18, 1959, and Serial Number 1,837, filed January 5, 1960, which are now abandoned.

The most idely used method for smelting iron ores is the reduction of these ores by means of coke in the blast furnace. Coke obtained by the high-temperature carbonization of coal in Dy-product coke ovens is the type of coke most extensively used. Only certain coals, referred to as coking coals, are suitable for producing coke having the desired physical and chemical properties for inwallurgical use. it is highly desirable, and frequently held essential, that the sulfur content of the coke to be used for metallurgical purposes be low. Thus a specification of the American Society for Testing Materials (ASTM Designation [3166-24) requires for the production of metallurgical coke that the composition of the coki g coal be such that the ry coke produced therefrom i ill not contain more than 1.0 percent of sulfur in the case of foundry coke and 1.3 percent of sulfur in the case of blast furnace coke. Under conventional hightemperature coking conditions, where the coking charge is essen ally a caliing coal of bituminous rank, the sulfur percentage of the coke obtained, based on the Weight of colic, is usually from 83 to 100 percent that of the sulfur percentage based on weight of the coal from which it was made. (Coke Evaluation Proiec (Iontrib. to lvietallurgy of Steel No. 43, Amer. Coke and Coal Chemicals inst, Washington, DC.) ()n this basis, coking coals of metallurgical grade may ordinarily not conmore than about 1.66 percent of sulfur. Inasmuch as reserves of such low-sulfur coking coals are limited, coals conta n 3g 1.5 percent or more sulfur, after washing must be blended low-sulfur coals in order to increase the total 1 ppiy available for producing metallurgical Thus 11inch of the metallurgical grade coke produced will have a sulfur content close to the maximum of 1.3 percent. 1 object of this invention effectively to provide nev "y ava -able reserves of metallurgical coal. ther obiect of the present invention to use fi iilg coal as a raw material for preparing hi strength metallu- 'ical fuel of substantially uniform size and shape.

it a 'urther object of this invention to provide a rocedure for producing desulfurized formcoke. a further object in using this simplified procedure to utilize coals having a sulfur content up to 2.2 percent by Weight or higher for preparing low-sulfur calcir formic-she of metallurgical grade.

it is still a further object o provide a sim ied method for th sirntut n and calc ng of coalchar agglorn It is yet an additional object to provide a simplified prowcure for obtaining significant desulfurization of ted agglcmer tes containing coal and fluidized lowtem; erature carbo'nization char, which procedure avoids the use of pressurized conditions. or devolatilization gas recycle.

in accordance with this invention, heat-processed'highsulfur content coal-char agglomerates are desulfurized to yield metallurgical grade formcoke prior to or concurrently With a calcining treatment. In a first aspect of this invention, a combined desulfurization and calcining treatment of the coal-char agglomerates is conducted in the presence of at least one atmosphere of hydrogen and in an environment having a volume ratio of H S/H less than 0.02. in a second aspect of this invention, the coal-char agglomerates are fed at atmospheric pressure in a descending column in countercurrent relation to autogenously produced devolatilization gas consisting principally of hydrogen. In both aspects of the process, the resulting desulfurized and calcined agglomerates are recovered as a metallurgical grade formcoke, preferably after being cooled below eir atmospheric kindling temperature.

The ag lomerates are preferably formed either as hottumbled coal-char agglomerates, preferably kiln-carbonized at a temperature above 800 F, or as briquetted coal-char agglomerates, preferably containing a pitch binder. The method of preparing hot-tumbled agglomerates will be hereinafter described. It is preferred, however, to prepare the coal-char agglomerates by briquetting, that is by an operation in which a press is used to effect cohesion and compaction of the fine particles or" coal and char. The addition of special binding materials such as pitch to the coal and char particles has been found to result in briquets of substantially improved strength when processed to formcoke. The pitch serves particularly as a temporary binder to provide adequate strength to the uncarbonized briquets to permit their ready handling before carbonization.

The coal-char agglomerates contain a caking bituminous coal and a low-density char, below about 45 pounds per cubic foot, obtained by a low temperature carbonization, i.e., at a temperature below 1400 F, of a caking bituminous coal. Either or both the caking bituminous coal and low temperature carbonization char may utilize low volatile, medium volatile, or high volatile coals, alone or in suitable admixture. In a particularly preferred feature of this invention, char having a poured bulk density less than about 30 pounds per cubic foot (ASTM test D29229) is obtained via a fluidized low temperature carbonization of a high volatile bituminous coal.

The coal-char briquets are shocltheated whereby their surface is rapidly elevated, virtually instantaneously, to a temperature of 9-30 to 1250 F. The surface of the briquets is maintained at a temperature of 900 to 1250 F. until they have attained throughout a temperature of 900 to 125-0 F. Thereafter the coked briquets are sub jected to a combined desulfurizing and calcining treatment whereby they are heated to a temperature above about 1550 F.

in a preferred embodiment of this invention utilizing these coal-char briquets, a high-sulfur, caking bituminous. coal or mixture of coals, preferably a high volatile cal-ling coal, and one havin an average sulfur content between about 1.6 and 5 percent by Weight, is converted to a finely divided char by low temperature carbonization. This carbonization is preferably performed under fluidized-bed conditions so as to yield a char having a bull; density less than about thirty pounds per cubic foot. 'With increasing bulk density, dcsulfurization becomes more difiicult. The carbonization temperature used to produce the char should ordinarily not exceed l400 F. The use of chars formed at substantially hi her temperatures w ll result in briquets yielding lesser amounts of devolatilization gas during the subsequent desulfurizing and calcining steps. Also, where the carbonization temperature exceeds 1400 F., the sulfur present in the char becomes chemically fixed and cannot be readily removed. The finely divided char is mixed with a portion of uncarbonized coal, and briquets are prepared from the resulting admixture. It is generally preferred because of the higher cost of char compared with coal to have the char content in the coal char briquets as low as possible. However, in order to provide briquets having sufiicient mechanical strength to yield formcoke suitable for use in a blast furnace, the char content of the coal-char briquets should ordinarily not be less than 40 percent by weight. Where optimum mechanical strength is not required, the amount of char in the coal-char briquet may be lowered, although this will tend to reduce somewhat the yield of devolatilization gas during the subsequent desulfurizing and calcining steps. Where a high-char content briquet is desired, the amount of char in the coal-char briquet may be increased to 90 percent without markedly lowering the strength of the ultimate formcoke. Increasing the char content beyond 99 percent results in a formcoke of insufficient physical strength for use in blast furnace opera tions.

To prepare low-sulfur calcined formcoke of metallurgical grade, i.e., one having suitable physical and chemical properties, the surface of these briquets is heated as rapid- -ly as possible, i.e., shock-heated, to a temperature in the range of 900 to 1250 F., and then the surface is further maintained at this temperature until the briquets attain a carbonizing temperature above 900 F. throughout.

Volatile materials that are evolved from the briquet are recovered as tar vapors and gases. In the shockheating treatment, tar vapors and a hydrocarbon-rich gas are the principal evolution products. This latter gas is generated in sutficient quantity to supply autogenously the hydrogen required in the process, thereby avoiding need of an extrinsic hydrogen supply.

We have successfully prepared metallurgical fuel according to our process from high volatile caking bituminous coal from the Pittsburgh seam having a sulfur content of 2.5 percent. The resulting metallurgical fuel had a sulfur content less than one percent and possessed density and strength characteristis comparable to acceptable metallurgical coke. In addition, our metallurgical fuel is produced in substantially uniform size and shape.

A brief review of the sulfur phenomena of coal will be of aid in appraising the environment of our invention, particularly with reference to the first aspect of our process.

There are two basic types of sulfur in coal and char which are usually referred to as the organic and inorganic sulfur. Organic sulfur is associated directly with the carbonaceous matter although the particular way in which it is bound is unknown. The removal of organic sulfur by hydrogen is a reversible reaction,

hydrogen is a reversible reaction, i.e., at relatively high ratios of hydrogen sulfide to hydrogen, sulfur is transferred from the gas phase to the carbonaceous solid phase. It is thus obvious that hydrogen sulfide is a strong inhibitor for removal of organic sulfur, and the volume ratio of HgS/Hg must be maintained at a low value for the desulfurizing action to proceed.

For any given set of conditions, there is a ratio of hydrogen sulfide to hydrogen at which there is no driving force for either removal or deposition of sulfur on the carbo naceous matter. This ratio determines the so-called point of total inhibition. The total inhibition ratio is a function of the desulfurization temperature, the total sulfur content and prior thermal history of the carbon. The ratio, for example, is relatively high for carbonaceous solids having relatively high sulfur content. We have also found that the ratio decreases according to the severity of the prior thermal treatment of the carbonaceous solids.

Severe thermal treatment also drastically reduces the rate at which the desulfurization reaction proceeds.

The total inhibition phenomenon shows the advantages inherent in a countercurrent process. The correlation of desulfurization rate with thermal history of the carbo naceous solids makes it imperative to conduct the calcining and desulfurization operations simultaneously. This feature is an inherent part of our invention.

Inorganic sulfur occurs in the form of several definite inorganic compounds. The major portion of the inorganic sulfur occurs in coal in the form of iron pyrites which is converted lar ely to ferrous stlfide by thermal transformation on heating to desulfurization temperature.

Removal of sulful from ferrous sulfide is a reversible reaction as in the case of the organic sulfur.

The equilibrium ratio of H S/H is in this case, however, a function only of the temperature and is independent of the amount of sulfur present. The value of the equilibrium ratio is considerably lower than that which applies to the removal of the bulk of the organic sulfur. The equilibrium value is, for example, 0.0012 at 1350 F. and 0.0028 at 1600 -F. Hence removal of sulfur existing as ferrous sulfide requires that the volume ratio HgS/Hz be less than 0.0012 at 1350 F. and less than 0.0028 at 1600" F.

Other types of inorganic sulfur such as calcium sulfide which are present in small quantities cannot be removed within practical limits by hydrogen. In addition, there is a small quantity of refractory organic sulfur of the order of O.30.5 weight percent of the carbon which cannot be removed by using practical quantities of hydrogen.

One method for maintaining a low value for the volume ratio H S/H is to supply sufficient quantities of hydrogen gas so that the sulfur removed from the briquets (as hydrogen sulfide) is less than two percent of the total hydrogen gas. Countercurrent movement of the hydrogen gas and the briquets undergoing desulfurizing treatment is desirable in this instance. The incoming gases, having a low volume ratio of H S/H contact briquets which already have lost the bulk of organic sulfur and hence the incoming gas can remove some inorganically bound su lfur. The existing gases, having absorbed H 5, thereafter contact incoming briquets which still contain the more readily removable organic sulfur which may be released into the exiting gases. This method, corresponding to that described in U.S. Patent 2,717,868, is employed in the embodiment of the present invention as shown in PEG- URE 4.

Another method for maintaining a low value for the volume ratio H S/H is to remove the hydrogen sulfide from the gas phase in situ as soon as it is formed. For this purpose, we adopt the process described in US. Patent 2,824,047 and employ solid acceptors for hydrogen sulfide.

These solid acceptors for hydrogen sulfide are materials which have a greater afiinity for hydrogen sulfide than those materials with which the sulfur is bound in the carbonaceous solid. The equilibrium volume ratio fi s/H for the acceptor solid at the desulfurizing temperature should be lower than the equilibrium volume ratio of the sulfur which is to be removed from the briquet. The solid acceptor, furthermore, should be resistant to abrasive degradation at elevated temperatures and must be capable: of being regenerated from its sulfur-containing form into. a state where it will once more absorb hydrogen sulfide.v The solid acceptors are capable of reacting with hydrogen sulfide to form solid sulfide in the presence of hydrogen. gas and also capable of rejecting sulfide sulfur under oxi-- dative conditions. A preferred acceptor for our desul-- furization process is lime in the form of calcined dolomite. Another preferred acceptor is manganese oxide impregnated on an inert carrier or in the form of manganese: ore. Other suitable acceptors include zinc oxide, nickel oxide, cobalt oxide, copper oxide, lead oxide, and iron oxide. Suitable porous carriers for these impregnated or:- ides include silica-alumina, silica, alumina, natural clay pellets, and the like. Amphoteric and acidic oxides may be employed as supports if regeneration CGHClIlIlOHS be selected to avoid excessive reaction between the impreghated acceptor ingredient and the support.

The acceptor solid may be represented generally by the term nietal Accordingl the acceptor solid removes hydrogen sulfide from the gas phase.

Metal oside+H Se Metal sulfide ki-I thereby forming metal sulfide and Water. The metal sulfide thereafter may be removed from the desulfurizing and regenerated to the oxide form by reaction with oxygen.

Metal sulfide +u ltletal oxide-+30 acceptor regs ration occurs at a temperature above the desurturizing temperature, and hence the regenerated acceotor may be recirculated througl the desulfur' ing zone to supply not only capacity for absorbing hydrogen sulfide but also to supply the thermal requirements of calcining.

For convenience in describing this invention, the proces employed herein has been divided into two dis nc aspects or" practice. it will be realized, however, that these two aspects l. ay be readily inter ningled, and various dentures characteristic of one may be used wit the other.

A first aspect of the process of this inv acterized by the use of pressurized cond' s, devolatilization gas recycle, and a very low ratio c- 3/3 For obtaining maximal desulfurization, the H S/H ratio may be further lowered by the use of H acceptors, hydrogen gas pressure may be increased, gas recycle be r ed, and the low temperature char selected for i the cod-char agglomerate will have a bull: density Well below 30 pounds per cubic foot.

In a second aspect of our process, in its roost simplified version substantial and significant desulin'ization is obtained Without the use of any pressurized equipment, and Without any external recycling of gas or external sulfurrernoval steps. This desulfurization is obtained by feeding the coal-char agglomerat s at atmospheric pressure in a descending column in counterc irent relation to an up T st eam of only in sit .-generated autogenous devolatuiz gas.

For a more comple e understandin of the present invention, its objects and features, reference should to the following detailed description and accent- "gs in which;

l is a so. ilow diagram indicating the processing steps involved in a first aspect of the process of the present invention;

FIGURES 2 and 3 are schematic flow diagrams lustrating alternative methods for conducting the shoclqheating stage of the present invention described in connection with l;

PZGURES 4 and 5 are schematic illustr native methods for conducting the corn. and desulfur ing treatments described in connection w.-.

l; and FIG 6 and 7 are schematic i ble as ores J6 ment of carbonized coo char agglomerates once with the aspect of the invention illustrated Z11 Cir FIGURE 11 is a schematic illustration of a unitary vessel for performing the several steps of the process of this invention in connection with FIGURE 8.

The coal-char agglornerates which are an essential feature of this invention, are preferably formed by either briquetting or hot-tumbling it is particularly preferred to prepare the coal-char agglomerates by briquetting, the several figures of the drawing Will be discussed with respect to the preparation and use of these briquets in the process of this invention. The alternative method of forming hot-tumbled coal-char agglomerates Will be subsequently described.

l. Pl'RST ASPECT GP PRGVESS A preferred embodiment of our present process will be described in detail by reference to FEGURE l. A cahing bituminous coal and preferably a high volatile coal from a source is provided as starting material. A portion of the high volatile coal is processed via fluidized low temperature carbonization in a zone 11 whereby the coal is converted into gas, tar and a porous fine.y divided solid distillation residue termed char. Char production from high volatile coals by fluidized low temperature carbonization processes is swelled and expanded from the original dimensions of the coal particles into fluffy, rounded particles. The sponge-like porous properties of the char particles result in a low bulk density of th material and a correspondingly low physical strength. The bulk density of the material is from about 20 to pounds per cubic foot. in general, the char is sufiiciently nnely divided, as produced, to pass through a 14 mesh Tyler standard screen. While it is possible to prepare high density char, i.e., above about 4-5 pounds per cubic foot, from high volatile bituminous coal by fluidized low temperature carbonizat-ion processes, such dense chars are not suiable in the present process.

Any low temperature carbonization process or type of caking bituminous coal may be used as long as the re- 1' possesses a low bulls density. Chars having a low bulk density that is less than pounds per cubic feet are produced, for example, from fluidized low temperature carbonization processes employing preliminary treatment of the coal, as by oxidation, to achieve operability. Char produced by fluidized low temperature carbonization permits the preparation of product metallurgical fuel having the strength and density corresponding to eic'sting coke oven products. In addition, the char produced by fluidized low temperature carbonization is peculiarly amenable to the desulfurization treatment or" the present invention,

finely divided product char is blended finely divided calzing bituminous coal in a briquet preparation zone 12 wherein substantially uniform sized o uets are prepared. In a preferred embodiment, the coal employed in the briquet preparation may be the S33E16 coal Which is employed in preparing the char via the fluid zed low temperature carbonization process. Alternatively, the coal employed in the briquets may be from a difieren-t source provided at the coal possesses K hl-y calzing properties. If desired, binder materials such as pitch may be employed in the briquet preparation stage to introduce shape retaining properties to the briquet prior to the subsequent processing.

The briquets are transferred from the briquet preparation zone 12, into a shockheatin and holding zone 13 for shockheating whereby their surface is virtually instantaneously elevated to a temperature in the range of 960 to 1250 F. The surface of the briq ets is retained at a temperature of 90C to 1250 F. until the briquets attain through-out a temperature of 900 to 1250 F.

The residence time of the briquets in the shockheating and holding zone 13 is from about 39 to minutes. Unless sufiicient residence time is provided for the briquets in the shoclcheating and holding zone 13, the further treatment will introduce serious cracks and fissures into the briquets resulting in a shattered product. As the dimensions of the briquets are increased, the residence time in the shockheating and holding zone 13 should increase. With small briquets (less than one inch diameter) the problem is not severe. However where larger briquets are being prepared (two inches diameter and larger) the holdup time is critical. We have prepared satisfactory twoinch diameter briquets by employing 30 to 45 minutes residence time at shockheating conditions. The briquets must not be heated beyond the shockheating temperature until their coal constituent has passed entirely through its plastic temperature range.

Although some of the heat required in the shockheating and holding zone may be supplied indirectly, we prefer to provide the bulk of the heat directly, either by means of hot gases as will be described in connection with FIG- URE 2 or alternatively by recirculation of finely divided heat carrying medium as will be described in connection with FIGURE 3. The resulting coked briquets are introduced into a calcining and desulfurizing zone 14 which is maintained under elevated temperatures suflicient to provide at least one atmosphere of hydrogen pressure. A pressure seal, indicated schematically by the numeral 15, is illustrated in one embodiment in FIGURE 6.

In this first aspect of the invention, the briquets fed to the desulfurizing and calcining zone 14 are elevated to a temperature above about 1550 F. directly by means of hot gases as will be described in connection with FIGURE 4 or, alternatively, by means of hot heat-carrying material as will be described in connection with FIGURE 5. While in the calcining and desulfurizing zone 14, the briquets are exposed to at least one atmosphere of hydrogen gas to effect the desired desuliurizing treatment. The volume ratio of H s/H is maintained below 0.02 to avoid suppression of the desulfurizing reaction. The volume ratio of H S/H can be maintained at a low value by providing suflicient hydrogen gas with external H 8 removal facilities as described in the aforementioned US. Patent 2,717,- 868. Alternatively, the volume ratio of H S/H may be maintained at a low value by providing in situ solid acceptors for hydrogen sulfide as described in the aforementioned US. Patent 2,824,047. In this latter embodiment the solid acceptors for hydrogen sulfide may serve also as the heat-carrying material. Concomitant devolatilization of the briquets occurs in the calcining and desulfurizing zone 14 to produce additional hydrogen gas which may be employed by appropriate recycle techniques in the process. The desulfurization process proceeds at an optimum rate in the temperature range 1300 to 1500" F. Prolonged exposure of the briquet at temperatures above about 15 00 F. adversely affects the attainable desulfurization reaction rate. Where desirable high strength properties in the solid product are sought, a final calcining temperature above about 1500 F. is required. Thus optimum results are obtained by conducting the desulfurization reaction principally while the briquets are being raised in temperature within the combined desulfurizing and calcining zone.

The resulting calcined desulfurized briquets are gradually cooled directly by means of a coolant medium in a cooling zone 16. The cooling treatment preferably is conducted at atmospheric pressures and may be eifected in part simultaneously with the transfer of calcined desulfurized briquets from the superatmospheric pressures existing in the calcining and desulfurizing zone 14 by means of the pressure seal apparatus schematically illustrated by the numeral 17 and further illustrated in our embodiment in FIGURE 7.

Hot gases entering the top of the vessel 20 pass downwardly through briquet bed 26. Initially the surfaces of the briquets are virtually instantaneously heated to a temperature in the range of 900 to 1250" F. This shockheating serves to form a crust of coked material around each individual briquet which provides shape retention for the briquets and avoids adherence of the briquets. Gases and tar vapors are evolved from the briquets under the thermal treatment and are swept along with the hot gases for recovery at temperatures of 1200 to 1600 F. through a conduit 31 near the bottom of the vessel 20. The tar vapors are processed for recovering the valuable tars and gases in a recovery zone 32. A portion of the gaseous product may be employed as the fuel gas in the present process as indicated by the conduit 33.

Starting with briquets prepared as hereinbefore de scribed, a typical distribution of the products of the shockheating and holding zone 26 is as follows.

Product: Weight percent Coked briquets 77.7 Tar vapors, water of formation and gas 22.3

The briquets leaving the shockheating zone through the opening 25 have been carbonized, freed of agglomerative tendencies and are at an elevated temperature in condition for the subsequent combined calcining and desulfurizing treatment of the present invention.

As an alternative to the embodiment illustrated in FIG- URE 2, which employs hot gases to supply the heat requirements for the shockheating and holding zone, we may provide the apparatus illustrated in FIGURE 3 wherein the heat requirements are supplied by recirculating finely divided fluidizable heat-carrying material through the shockheating and holding zone. The finely divided fluidizable heat-carrying material preferably is finely divided sand or finely divided low temperature carbonization char.

As shown in FIGURE 3, a shockheating and holding vessel 40 is provided having vertical side walls 41, a top wall 42 and a bottom wall 43. An opening 44 is provided in the top wall 42 to permit introduction of briquets at a temperature below the plastic temperature of their coal constituent. An opening 45 is provided in the bottom wall 43 for discharging coked briquets from the vessel 40. The vessel 4%) is adapted to confine a downwardly moving fixed bed 46 containing briquets in particle-to-particle contact. The vessel 40 is further adapted to confine a fluidized mass of heat-carrying material maintained in random motion through the interstices existing between the briquets under the influence of upwardly moving fluidizing gases. The heat-carrying material passes countercurrently to the moving bed of briquets. A complex flow pattern is established wherein a dense fluidized phase of heat-carrying material is maintained in the large void spaces between the briquets. Heat-carrying material is transferred between these small pseudo-fluidized beds as a disperse phase.

Heated heat-carrying material is introduced into the vessel 4% through a conduit 47 as a disperse phase suspended in an inert carrying gas. Upon entry into the vessel 49, the inert carrying gas becomes a portion of the fiuidizing gas required to maintain the random motion of the fluidizable heat carrying material therein. An overflow Weir 48 or similar apparatus is provided near the top of the 'essel it? to collect finely divided heat carrying material for recovery through conduit 49 and ultimately reheating in an external fluidized heating vessel 50. The heat carrying material is entrained in a stream of gas, preferably air, from a conduit 51 and introduced into the heating vessel 59 maintained at a temperature above the desired shoclrheating temperature or the vessel 4%. The heat required for reheating the heat-carrying material may be supplied by passing hot gases through the heating vessel 55) or by burning a fuel within the vessel 59. The recirculating stream of heat-carrying material will contain a quantity of carbonaceous material abraded from the briquets which may be burned with air in the vessel to supply the heat. If low temperature carbonization char is the heat-carrying material, it may be partially burned in the vessel 5!} to supply the heat. This lastrnentioned technique requires provision of a source of make-up char required to replace that lost by partial combustion. Suriicient carbonaceous material may be abraded from the briquet surfaces to provide a portion of the make-up char required to compensate the heatcarrying material destroyed by partial combustion.

A cyclone 52 is provided in the heating vessel 50 to separate entrained solids from the spent gases which are discharged through a conduit 53. Heated heat-carrying material is withdrawn from the heating vessel 50 through a conduit 54 and reintroduced into the shockheating and holding vessel 40 through the conduit 47 as described.

Additional fiuidizing gas may be introduced into the shockheating and holding vessel 40 through a conduit 55 having a plurality of distribution inlets 56 through the bottom wall 43. A cyclone separator 57 is provided in the vapor space above the bed '46 to remove entrained solids from the spent gases and evolved tar vapors which are recovered virtually free of solids through a conduit 58 for recovery of valuable tar products and gases in a tar recovery zone 59.

Starting with briquets prepared as hereinbefore described, a typical distribution of the products of the shockheating and holding zone 40 is as follows.

Product: Weight percent Coked briquets 76.2 Tar vapors, water of formation and gas 23.8

The heat-carrying material enters the shockheating and holding vessel 40 through the conduit 47 at a temperature of 1200 to 1500 F. The heat-carrying material leaves the shockheating and holding vessel 40 through the conduit 49 at a lower temperature, for example, 900 to 1250" F. The temperature differential between the heat-carrying material in the conduit 47 and in the conduit 49 will determine the quantity of heat-carrying material required to effect shockheating and coking of the briquets in the bed 46.

A small quantity of stripping gas is introduced into the discharge opening 45 through a conduit 60 to strip the finely divided heat-carrying material from the surfaces of the coked briquets being discharged through the opening 45.

We prefer to employ low temperature carbonization char produced by fluidized processes as the heat-carrying material since any adhesion of the solids on the surfaces of the briquets will not contaminate the ultimate product. However, even where sand is employed as the heatcarrying material, we have found that adhering particles of sand comprise less than one percent of the weight of product briquets.

We have found that a movement of about 2 to pounds of fiuidizable char per pound of briquet through the shockheating and holding vessel 49 is satisfactory for the shockheating requirements.

Referring now to FIGURE 4, we have illustrated apparatus suitable for conducting the calcining and desulfurizing treatment of the present process employing heated hydrogen gas as the heating agent and desulfurizing agent for the briquets. A calcining and desulfurizing vessel 70 is provided having vertical side walls 71, a top wall 72 and a bottom wall 73. An opening 74 is provided in the top wall 72 for introducing coked briquets at a shockheating temperature into the vessel 70. An opening 75 is provided in the bottom wall 73 for discharging calcined desulfurized briquets. The vessel 70 is adapted to confine a downwardly moving bed 76 of briquets in particle-toparticle contact. The briquets may be introduced into the vessel 7!} through the opening 74 either continuously or batch-wise. A residence time of about one to three hours within the vessel 70 is preferred.

Heated hydrogen gas at a temperature of about 1600 1800 F. is introduced into the bottom of the vessel 70 through a conduit 77. The heating gas may include other non-oxidizing gases such as carbon monoxide and methane provided the partial pressure of hydrogen exceeds one atmosphere. The entering gas should be virtually free of hydrogen sulfide. Where, as illustrated in FIGURE 4, a direct gas calcining and desulfurizing sys- 3% tem is employed, the partial pressure of hydrogen preferably is in excess of one atmosphere, for example, 3 to 10 atmospheres.

About 10 to 30 standard cubic feet of hydrogen are passed through the calcining and desulfurizing vessel 79 for each pound of briquets. The sensible heat of the gas is employed to raise the temperature of the briquets above 1550 F. In addition, the hydrogen reacts with the sulfur of the briquets to form hydrogen sulfide. The quantity of hydrogen required to effect desulfurization is more than sufficient to provide the sensible heat required for the calcining at readily attainable preheat temperature levels. In any event the quantity of hydrogen should be suflicient to effect desulfurization of the briquets without exceeding a volume ratio of H S/H greater than 0.02 within the vessel 70. The desulfurizing duty of the hydrogen gas increases with increasing sulfur content of the briquets. The additional heating of the briquets in the vessel 7% results in further devolatilization and net production of hydrogen gas which may be retained and recirculated in the system for further processing of briquets.

Hydrogen gas passes upwardly through the briquet bed 76 and is removed through a conduit 78 from the top of the vessel 70. The gases are preliminarily cooled in a heat exchanger 79, further cooled in a cooler 80 and substantially freed of hydrogen sulfide content in an H 5 removal system 81. The H 8 removal system may employ, for example, the well-known diethanolamine process, a solid hydrogen sulfide acceptor process, or any convenient means.

Cooled hydrogen, virtually free of hydrogen sulfide, is recovered from the removal system 81 through a conduit 82, compressed to the desired pressure in a compressor 83, preliminarily heated by heat exchange in the exchanger 79, and introduced into a high temperature heater 84. The high temperature heater 84 is shown as a checkerwork regenerator which is well suited for the purpose. Fuel and air may be supplied to the heater 84 through conduits 85' and 86 respectively during off cycles in a wellknown manner.

Net product gas containing hydrogen may be recovered through a conduit 87.

The desulfurizing action described in connection with FIGURE 4 corresponds in detail to that disclosed in the aforementioned US. Patent 2,717,868.

The following examples are illustrative of this invention, particularly with reference to a first aspect of the process of this invention. However, these examples are not intended to restrict the scope of this invention as previously described. Thus it will be readily apparent that those phases of the examples dealing with agglomerate preparation and shock-heating of briquets are generally equally applicable to the second aspect of this invention to be hereinafter described.

Example I Briquets which were prepared as described from Ari:- wright coal, a typical Pittsburgh seam bituminous coal, contained 2.20 percent sulfur. The briquets had been prepared from the following formulation in cylindrical shapes, 2 inches diameter by 2% inches high.

Ingredient: Percent by Weight (a) Arkwright coal 25.0 (b) Char produced by fluidized low temperature carbonization of Arkwright coal 58.5 (0) Low temperature carbonization pitch 5.3 (d High carbon content pitch 6.2 (e) Recycle coke particles 5.0

The briquets were shockheated and held at 950 F. in a fluidized bed of sand for 30 minutes. Thereafter the briquets were heated at about 6 to 8 F. per minute to a temperature of 1600" F. in an atmosphere of 30 p.s.i.g. hydrogen. The product briquet had a sulfur content of 1.214 percent after one hour exposure at 1606' F.

1 1 Example I] Briquets having one inch diameter were prepared from Arkwright coal and char obtained by fluidized low temperature carboniZat-ion of Anhwright coal in the proportions shown in Example I. The briquets contained 2.30 percent sulfur. Following shockheating at 110C- F. in a fluidized bed of sand, the briquets were retained at 1100'" E. for 30 minutes and thereafter heated to 1600" F. at about 8 to 10 F. per minute. The briquets were retained at 1660' P. for one hour at a pressure of six atmospheres absolute of hydrogen gas. The product briquets had a sulfur content of 0.51 percent. The product briquets had a cold tumbler index, /z-inch (a measure of strength), of 83% which is considered good.

In place of Arkwright coal, an acceptable char possessing a desired bulk density of less than about 30 pounds per cubic foot may be prepared by the low temperature carbonization of a low volatile bituminous coal such as Pocahontas seam coal or from a high-sulfur medium volatile Kittanning seam coal.

FIGURE illustrates apparatus adapted for conducting the calcining and desulfurizing treatment according to the teachings of the aforementioned U.S. Patent 2,824,047. According to this alternative technique, finely divided particles of fluidizable solid materials (termed hydrogen sulfide acceptors) are used to supply the heat required for calcining and to remove hydrogen sulfide from the vapor phase to maintain the volume ratio of H S/H at a low value. The acceptor solids preferably comprise lime or manganese oxide. The active ingredient of the acceptor solid may be impregnated upon abrasion resistant particles of refractory material.

As shown in FIGURE 5, a calcining and desulfurizing vessel 99 is provided having vertical side walls 91, a top wall 92 and a bottom wall 93. A conical grid element 94 having a central opening 95 is provided within the vessel 9 to separate its interior into an upper chamber 96 wherein calcining and desulfurizing occur and a lower chamber 97 wherein desulfurized calcined briquets are partially cooled and incoming hydrogen gas is preliminarily heated. An opening 98 is provided in the top Wall 92 for introducing coked briquets at an elevated temperature into the vessel 99. An opening 99 is provided in the bottom wall 93 for discharging calcined desulfurized briquets. A downwardly moving bed of briquets is maintained in the chamber in particle-toparticle contact. Finely divided fiuidizable acceptor solids are introduced into the chamber 96 as a suspension in hydrogen gas through a conduit 180. Additional hydrogen gas for fiuidizing and desulfurizing is intro duced into the lower chamber 97 through a conduit 191. Under the fiuidizing influence of upwardly moving hydrogen gas, the fluidizabie acceptor solids are maintained in random motion through the interstices existing between the briquets in the chamber 96. An overflow weir 192 is provided in the upper portion of the chamber 96 for recovery of acceptor solids. Relatively cooled acceptor solids, containing sulfur which they have absorbed in the chamber 96 are recovered through a conduit 1% and, suspended in a stream of air from a conduit 164, are introduced into a regenerator vessel 1415 for elimination of sulfur and reheating. Spent fluidizing gases containing sulfur dioxide are discharged from the vessel Hi5 through a conduit 1435. Regenerated acceptor, at a temperature of about 1600' to 1800 F., is recovered through a conduit 167 for reintroduction into the treating chamber 96. The regenerated acceptor has renewed capacity for absorbing sulfur in the treating chamber 96.

Spent fluidizing gases comprising hydrogen are freed of entrained solids in a cyclone separator 1&8 provided in the vapor space above the treating chamber 96 and are recovered virtually free of solids through a conduit 109. The gases in conduit 1%? are virtually free of hydrogen sulfide, i.e., they contain only that quantity of hydrogen sulfide which exists in equilibrium with the particular acceptor employed in the process. Hence the gases in the conduit 1G9 may be recycled directly through a conduit 119, repressurized in a compressor i111 and reemployed in the process. The net gases resulting from devolatilization of the ooked briquets in the chamber 96 may be withdrawn through a conduit 112.

The briquet cooling chamber 97 serves for partially cooling the product briquets and partially preheating the hydrogen employed as fluidizing and treating gas. A small quantity of gas, e.g., hydrogen-rich gas, may be introduced through conduit 113 into the discharge opening 9 to strip product briquets of any adhering particles of the finely divided acceptor.

We have found that about 2 to 5 standard cubic feet of hydrogen per pound of briquets is satisfactory in this system. We have also'found that when lime or manga nese ore is employed as the acceptor solid, the desulfurizing capacity of the solid greatly exceeds the desulfurizing duty when the acceptor is employed in suificient quantity to provide the heat necessary in the process.

Example HI Briquets were prepared as described in Example I. The sulfur content was 2.20 percent. The briquets were shockheated to 950 F. in a fluidized bed of sand and maintained at 950 F. for one-half hour. Thereafter the briquets were heated to 1350 F. and treated in the presence of fluidized acceptor solids with hydrogen gas as the fiuidizing gas (superficial linear velocity of 0.4 foot per second) at a pressure of one atmosphere and at a pressure of three atmospheres. The acceptor solids were alumina pellets impregnated with 8 percent of manganese oxide. The sulfur content of the resulting formcoke is listed in Table I (A) for treatment at one atmosphere hydrogen pressure and three atmospheres hydrogen pressure.

Example IV Briquets were prepared and treated as in Example 111 except that the desulfurization was carried out at 1450" F. The sulfur content of the resulting formcoke is listed in Table I (B) for treatment at one atmosphere hydrogen pressure and at three atmospheres hydrogen pressure.

TABLE I.-DESULFURIZATION OF BRIQUETS 1 Sulfur Content of Product Briquets, Weight Percent Length of Treatment, Hours At 1 atm. At 8 atm. Hydrogen Hydrogen (A) At 1,350 F.:

1 In examples III and IV the combined dcsulfurization and calcining step was terminated at 1350 Rand 1450 F.respectivelyin a deliberate attempt to demonstrate the cfiect of temperature on the desulfurization phase alone. Hence Example III may be considered as including a partial dcsulfurization and partial calcining step whereas Example IV ntlay be considered as including a dcsulfurization and partial calcining s ep.

Referring now to FIGURE 6, we have illustrated a lock hopper system suitable for use as the pressure seal 1'5 illustrated in FIGURE 1. Such a lock hopper system would handle briquets being discharged from the shockheating and holding zone, as for example, through the opening 25 in FIGURE 2 or the opening 4-5 in FIGURE 3. The lock hopper system would provide briquets at an elevated pressure for introduction into the calcining and desulturizing zone.

As shown in FIGURE 6, two lock hopper surge vessels 12 i; and 121 are provided having inlet conduits 122 and 123 respectively joining with a briquet inlet conduit 124. The lock hopper surge vessels 12d and 121 have briquet discharge conduits 125 and 126 respectively joining a conduit 127. Coked briquets at a shoclLheating temperature are introduced into the conduit 124 and are alternatively deposited in the surge vessel 120 or 121. When the vessel 12% is receiving briquets from the conduit 124, a valve 125a in conduit 125 and a valve 123a in conduit 123 are closed. During this time a valve 122a in conduit 122 and a valve 1250 in conduit 126 are opened. Accordingly, the surge vessel 120 is maintained at the same pressure as the shockheating and holding zone. The surge vessel 121 is maintained at the same pressure as the calcining and desulfurizing zone. When the inventory of briquets in the surge vessel 120 is full and the inventory of briquets in the surge vessel 121 has been depleted, the valves 122a and 126a are closed and the valves 123a and 125a are opened for the alternative half-cycle.

Referring to FIGURE 7, we have illustrated apparatus adapted to serve as a pressure seal 17 (FIGURE 1) between the calcining and desulfurizing zone and the cooling zone. Two lock hopper surge vessels 13% and 131 are provided having inlet conduits 132 and 133 respectively at their tops connected to a briquet conduit 134 and having discharge conduits 135 and 136 respectively connected to a briquet discharge conduit 137. The briquet conduit 134 would join, for example, the conduit 75 of FIGURE 4 or the conduit 99 of FIGURE 5. During one-half cycle a valve 132a in conduit 132 is open, a valve 133a is conduit 133 is closed, a valve 135a in conduit 135 is closed, and a valve 13611 in conduit 136 is open. During this half-cycle briquets are discharged into the surge vessel 13$ through the conduits 134 and 132. During the initial portion of this cycle a cool gas may be introduced from a manifold conduit 133 into the surge vessel 131 containing hot product briquets. The cool gas is itself heated by removing heat from the briquets and is recovered through conduits '141 and manifold conduit 143. Desirably a cool fuel gas may be employed for this purpose and be preheated for combustion thereby.

During the alternate half-cycles the valves 132a and 136:: are closed and the valves 133a and 13a are open, thereby maintaining the superatmospheric pressure existing in the calcining and desulfurizin zone. Product briquets are recovered through the briquet discharge conduit 137.

It should be apparent that either of the embodiments of shockheating and holding treatment illustrated in PEG- URES Z and 3 may be employed with either of the embodi'nents of desulrurization and calcining treatment illustrated in FIGURES 4 and 5. Where higher press res of hydrogen are employed, for example, atrno or more for the desulfurization treatment, the Ir gas preferabl will contain substantial quantities of methane to avoid carbon loss from the briquets by hydrogenation.

c-q-ni cn,

If Jfiicient methane is maintained in the recirculating gas stream, its presence Will suppress the carbon hydrogenation reaction without adversely affecting the desired desulfurization reaction. The volume ratio of CA L/H preferably is from about 0.04 to 0.30.

H. SECOND ASPECT OF THIS lNVENTiON In a preferred version of the simplified second aspect of this invention, the coal-char briquets are shock-heated and carbonized at a temperature in the range of 900 to l250 1 They are next heated from a temperature below 1300 F. to a temperature above 1550 F. while feeding them at atmospheric pressure in a descend ng column in countercurrent relation to an upwardly moving stream of gas containing autogenous devolatilization gas. The total gas pressure is essentially atmospheric. Use of only the autogenous devolatilization gas at atmospheric 14 pressure will effect substantial desulfurization. To increase the amount of desu-lfurization, a desulfurizing gas such as hydrogen may be externally fed to this system and recycled therein, even at substantially atmospheric pressure. Such a recycle technique will be effective only where the hydrogen sulfide that is formed is absorbed in situ by acceptors or is removed externally. However, in the simplest aspect of this invention, substantial desulfurization is obtained when the brique'ts are fed at atmospheric pressure in countercurrent relation to an internal upwardly moving gas stream consisting essentially :of autogenous devolatilization gas. The briquets are then recovered as a low-sulfur calcined formcoke of metallurgical grade ideally suited for use in a blast furnace. By atmospheric pressure is meant ordinary ambient air pressure, which of course varies from day to day at the same location. In feeding the briquets to the system at atmospheric pressure, this means that the pressure will necessarily vary slightly at other points in the system because of pressure drops due to the passage of desulfurization gases through the system. Thus a pressure slightly in excess of atmospheric pressure will ordinarily exist at the point of Withdrawal of the briquets from the system.

It is a surprising feature of this invention that substantial desul'furization is obtained in this process, even Where the desulfurizing and calcining treatment is carried out Without the use of any pressurized equipment, i.e., under atmospheric conditions, and without any external recycling of gas or external sulfur-removal steps. The process, in its simplest form, avoids any external feed of desulfurizing gas. it does not require the critical maintenance of a specific Pi s/H ratio. Significant desulfurizing action occurs as a result of contact only with the internal autogenous devolatilization gas which is movin up- Wardly in countercurrent relation to the downwardly moving agglomerates. it has been surprisingly and unexpectly found that, despite the consistent teaching contained in this long-established art to the effect that under coking conditions the sulfur content by weight of the coke will be from 89 to percent of the sulfur content by weight of the starting coal, the present process yields a desulfurized forrncoke having a sulfur content as loW as 59 percent by Weight compared with the percentage of sulfur in the coalchar feed. it is considered essential in effecting significant desulfurization by this second aspect of t= e process of this invention that the internal autogenous devolatilization gas not be diluted by inert gases. Thus the heat provided to the desulfurizing and calcining zone is supplied preferably by indirect means, i.e., by heating the walls of the vessel in which the reaction is to take place. Alternatively, this heat may be provided by transfer from circulating nonreactive solid particles such as char or sand as heat ca iers. The use of inert flue gases to provide the heat for the desulfurizing and calcining zone is to be avoided because of their diluent eliect on the autogenous devolatiliz tion gas. it it is desired to use hot gases to provide tie required heat in the desulfurizing and calcining zone, these gases must consist essentially of desulfurizin gases containing substantial quantities of hydrogcn.

FIGURE 8 is directed to a preferred embodiment of a second aspect of the process of this invention in which the use or" pressurized conditions or devolatilization gas recycle, as described in the first aspect of this invention, is avoided. Referring to PlGURE 8, high-sulfur caking coal from a source 2.1% is provided as starting material. This coal preferably has a sulfur content between about 1.6 and 2.2 percent by weight. A portion of the eaking coal is processed via low-temperature carbonization in a zone 211 whereby the coal is converted into gas, tar, and char. With preferred fluidized low-temperature carbonization processes, the char particles have a bulk density of about 20 to 25 pounds per cubic foot. In general, the char is sufficiently finely divided as produced, to pass through a i l-mesh Tyler standard screen. Char produced by fluidized low-temperature carbonization permits the preparation of product metallurgical fuel having the strength and density corresponding to existing coke oven products. In addition the char produced by fluidized low-temperature carbonization is perculiarly amenable to the desulfurlzation treatment of the present invention. It is preferred that the carbonization be performed at a temperature not exceeding 1490" P. so as to have a subsequent maximum yield of devolatilization gas.

As schematically illustrated in FIGURE 8, the finely divided product char is blended with finely divided calting bituminous coal in a briquet preparation zone 212 wherein substantially uniform sized briquets are obtained. The coal employed in the briquet preparation may be the same coal which is employed in preparing the char via the low-temperature carbonization process. Alternatively, the coal employed in the briquets may be from a diiferent source provided that the coal possesses highly caking properties. It is generally preferred that binder materials such as pitch be employed in the briquet preparation stage to introduce shape-retaining properties to the briquet prior to the subsequent processing.

The briquets are transferred from the briquet preparation zone 212 into a shock-heating and holding zone 213 for shock-heating whereby their surface is rapidly elevated, virtually instantaneously, to a temperature in the range of 960 to J250 F. The surface of the briquets is maintained at a temperature of 900 to 1250 F. until the briquets attain throughout a temperature of 900 to 1250 F., thereby being carbonized.

The residence time of the briquets in the shock-heating and holding zone 213 is usually from about 36 to minutes. The briquets must not be heated beyond the shock-heating temperature until their coal constituent has passed entirely through its plastic temperature range.

While some of the heat required in the shock-heating and holding zone may be supplied indirectly, preferably the bulk of the heat is provided directly either by means of hot gases in contact with the briquets or by circulation of finely divided heat-carrying solids.

The process thus far described with respect to the second aspect of this process is generally similar to that shown in FIGURE 1 with respect to the first aspect of this process. However the desulfurizing and calcining treatment of the colred briquets in this second aspect differs from the first aspect of the process with respect to the simplicity of procedure involved and the nonetheless substantial improvement in desulfurization obtained.

Referring again to FIGURE 8, it has been surprisingly found that the carbonized coal-char briquets from zone .213 may be simply treated at atmospheric pressure in the absence of gas recycle or acceptor recycle to provide a desulfurized formcoke having a sulfur percentage between 60 and percent of that in the feed briquet. This is accomplished in the desulfurizing and calcining zone 214 by heating the carbonized briquets to a temperature from below 1300 F. to above 155G E, preferably by indirect heating means, so that autogenous devolatilization gas is obtained. This gas consists principally of a mixture of hydrogen and methane. While being so heated, the briquets are fed in a descending column in countercurrent relation to the upwardly moving stream of autogenous devolatilization gas. No pressure equipment is :used or required, the reaction being performed at atmospheric pressure.

Direct heat may be provided to the briquets without interfering with the desulfurization reaction where a heating gas consisting principally of hydrogen is used. However, inert heating gases may not be used to provide the required heat in the desulfurizing and calcining zone 1214. Such gases will have a diluent effect with respect to the autogenous devolatilization gas, decreasing the desul- :furization obtainable. The heat may also be supplied by t-ransfer from unreactive solid particles as heat carriers.

furthermore, the volume ratio of H S/H need not be maintained below 0.02. -Even when the ratio is above this fig re, the desulfurization is not suppressed. Because the total gas pressure is atmospheric, that of the hydrogen gas present will be less than one atmosphere. Also, recycle is not required in order to maintain the HgS/Hg ratio to a critical value, nor is it necessary to provide in situ solid acceptors for the hydrogen sulfide to provide this ratio. In general, the desul-furization process proceeds at an optimum rate in the temperature range 1300 to 1500 F. although desulfu-rization continues up to calcining temperatures of 1800 F. Rapid eating of the briquets to temperatures above about 1500 F. may adversely affect the attainable desulfurization reaction rate.

ere desirable high strength in the solid products is sought, a final calcining temperature above about 15SO F. is required. Thus optimum results are obtained by conducting the desulfun'zation reaction principally while the briquets are being raised in temperature as they are moving downwardly in countercurrent relation to the upwardly moving devolatilization gas. A residence time of from one to about 2 hours at a temperature between 1300 and 150=0 F. is considered sufficient to ellect substantial desulfurization. A further residence time of between 30 minutes and about one hour at a temperature between 1550 and 1800 F. is sufficient to efiect calcining and also some additional desuliurization. For optimum desulfurization, a total time of about four hours within the desulfurizing and calcining zone is preferred. The resultant calcined desulfurized briquets are gradually cooled directly by means of a coolant medium in a cooling zone 15. The cooling treatment is also conducted at atmospheric pressure. The preparation of the briquets and their thermal treatment regimen is more fully described in the applications Serial No. 635,277, filed January 22, 1957, now abandoned, and Serial No. 635,421, filed January 22, 1957, now U.S. Patent 3,018,227, both assigned to the assignee of this invention.

Referring to FIGURE 9, a graphical comparison is shown of the desulfurization obtained with the two aspects of this process compared with that obtained in conventional high-temperature coke-oven processes. The two uppermost horizontal bars in FIGURE 9 show the improvement in sulfur content that may be expected in the carbonization of coal to produce product coke in conventional beehive and by-product coke ovens. In general, a sulfur content of 1.3 percent in the coke is considered the maximum permissible amount for use in the reduction of iron ore by conventional techniques in a blast furnace. Where the coke contains higher amounts of sulfur, then special desulfurization techniques applied to the hot metal after it leaves the blast furnace will be required.

In high-temperature coking, ordinarily up to about 45 percent of the sulfur present in the coal is evolved. The sulfur percentage of the coke corresponds to about to percent of the sulfur percentage of the coal prior to coking. Many attempts have been made to increase the desulfurization by causing a greater evolution of the sulfur in the volatile material, compared with the coke residue, during the coking process. Few if any practical results have been obtained from these extensive attempts. At present, as practiced on a commercial basis, the sulfur percentage of the high-temperature coke, on a weight basis, averages about 82 percent that of the sulfur percentage of the coal from which it is derived. In studies made of commercial coking practices, it was found that the percentage of sulfur in dry coke could be represented by the following equation proposed by Lowry et a1. (cited in previously mentioned Coke Evaluation Project):

(Sulfur in coke):0.084+0.759 (sulfur in coal) aspect of the process set forth herein is employed. In this first aspect of the process, coals having sulfur contents of 3 percent and higher may be successfully desu lfurized. However, to achieve this marked reduction in sulfur content, superatmospheric conditions must be employed wherein the partial pressure of the hydrogen in the gas is greater than one atmosphere, and wherein the volume ratio of H S/H is less than 0.32. Furthermore, recycle conditions and removal of sulfur either by use of acceptors or externall are required to efiect substantial reduction from high sulfur levels.

The lowest set of horizontal bars in FIGURE 9 shows the specific area for which the second aspect of the process of the present invention, uniquely adapted. Employing the second aspect of the process or" the present invention, desulfurized form coke having a sulfur content of 1.3 percent or lower may be obtained starting with a caking coal having a sulfur content as high as 2.2 percent, or even higher Where the char is preliminarily desulfurized. Thus this second aspect of the pro ass is particularly useful and preferred where the sulfur content of the starting coal is not greatly in excess of 2.2 percent, and where a reduction of 60 to 70' percent in the sulfur content of the coal-char aggregates is suflicient.

:In practicing this second aspect of the process of the present invention, there is effectively made newly available as metallurgical coal those coals having a sulfur content between 1.60 and 2.2 percent or higher. Inasmuch as lowsulfur coals, i.e., those having a sulfur content below 1.6 percent are becoming scarcer, this becomes a significant contribution in effectively providing newly available metallurgical coking coal reserves. In following this second aspect of the process of this invention as illustrated in the embodiment of FIGURE 8, starting with a coal having a sulfur content, for example, of 2.2.2..4 percent, a char is obtained having approximately 96406 percent of the percentage sulfur content of the starting coal. Thus a char having a sulfur content of approximately 2.2 percent is obtained. The briquets formed by blending the coal and char with pitch and breeze coke are still lower in sulfur content than the starting coal because of the low-suifur content of the added pitch and breeze coke. After treatment according to the embodiment of this invention as illustrated in FEGURE 8, product desulfurized for-mcoke having a sulfur content or" approximately 1.3

ercent by weight is obtained.

In .TlGU-RE it) is illustrated an indirectly heated retort adapted to the practice of the aspect of this invention illustrated in FEGURE 8, particularly for the treatment of prior carbomzed aggiorneratesv Brlquets that have been shock-heated and held for a suitable period of time are placed in feed hopper 216. The wall 217 of the furnace is made of a suitable refractory material such as silica brick or carborundtnn brick in order to withstand the high temperature require The desulfurizing and calcining zone 238 of toe furnace is conveniently heated by incandescent as which be fed through burner ports 2 9, as shown. The carbonized briquets contained in hopper are are fed into Z011 2113 where they are brought to an ultimate temperature above l559 F. As the coal-char agglomerates are gradually fed in a downward direction, increasing in temperature from below 1300 F. to above 1550- F autogenous gas is evolved. This gas, which is generated by the aforesaid heating of the coal-char particles, rises in a countercurrent direction to the movement of the feed, being at atmospheric pressure, and is removed through vent 22% The gas used to keep the furnace at temperature is vented through stack Z21. Thermocouples 222 are maintained throughout various critical areas of the furnace for controlling the temperature therein. The lower portion 223 of the furnace is cooled by circulating cooling water through jacket 224. The cooled desulfurized briquets collect in this lower portion and may be removed through gate 225.

In FIGURE 11 is shown a schematic view of a unitary furnace adapted for converting uncarbonized agglomerates to desulfurized formcoke in accordance with the aspect of the present invention illustrated in FIGURE 8. Uncarborn'zed bn'quets 22s are fed into a shock-heating and holding zone 22? which is directly heated by hot flue gas fed through a conduit 223. Cooled flue gas and minor amounts of volatile coke products are removed through a conduit 229. The desulfurizing and calcining zone 234i is indirectly heated as the b-riquets are passed downwardly through the furnace. A high Btu. content gas and other volatile coke products are evolved through conduit 231. The desulfurizing and calci ing zone 23b is maintained at atmospheric pressure, and the evolved autogenous gas generated serves as a desulfurizing gas by passing in a counter-current upwardly moving direction with respect to the downwardly moving cored briquets, which are being heated from a temperature below 1300" P. to above 1550= F. The product desulfurized forrncoke is collected after passing through cooling zone 232.

A. DESULFURIZATEON OF BRIQUETS Step 1Brz'quet preparatiorL-While this invention is broadly directed to the desulfurization of coal-char agglomerates composed of bituminous coal and low-density clar prepared by the low-temperature carboniZ-ation of bituminous coal, in its preferred aspects it is particularly suitable to the desulfurization of briquetted ag'glomerates which are formed from a mixture of a caloing bituminous coal and fluidized low-temperature carbonination char. The char in its preferred form is finely divided and has a bulk density less than about 30 pounds per cubic foot, being obtained by the low-temperature carbonization under fluidized conditions of, preferably, a high-volatile caking coal. The caliing coal used for preparing char is conveniently used for blending therewith. In the copending application of K, Baum and R. l. Friedrich, Serial No. 635,421, filed lanu-ary 22, 1957, now U.S. Patent 3,018,227, and assimied to the assignee of this application, are described methods for preparing briquets particularly suitable for use in the practice of this invention. A particularly preferred hriquet formulation comprises at least three ingredients which include a calcing bituminous coal, a low-temperature carbonization char that has been obtained by the fluidized low-temperature carbonization of a caking bituminous coal, and a pitch binder obtain d by the pyrolytic treatment of carbonaceous solid fuels, at least a portion of which has a fixed carbon content exceeding 25 percent. This mixture of stafiing materials is blended, kneaded and briquetted under pressure to uniform shape. Such briquets possess a satisfactory raw strength which is necessary to permit their being handled and moved in coking apparatus. Various shapes of briquets may be used depending upon the temperature, treatment and the type of furnace employed. Briquets which are dished, spheroidal, eggshaped (prol-ate spheroids) lenticular, gibbous or cylindricm in form may be employed. A particularly preferred briquet formulation consists of: 25 percent of a high-volatile caking bituminous coal, 58.5 percent char repared by the fluidized low-temperature carbonization of the foregoing coal, 6.2 percent recycle pitch, 5.3 percent pitch obtained from the low-temperature carbonization of bituminous coal and 5.0 percent recycle col; breeze. In general, it has been found that increasing the char content and lowering the coal content results in a weakening of the briquet. However, it has been found that briquets having a tumbler index strength in excess of percent may still be obtained where a formulation such as one containing 15 percent coal, 68.5 percent char, 5.0 percent recycle coke, 6.2 percent recycle pitch and 5.3 percent low-temperature carbonization pitch is employed. The tumbler index was obtained by a tumbler test which is a modified form of the standard tumbler test for coke (ASTM 13294-50). Normal by-product oven coke shows a tumbler index by our method in the range 88-9'4. In general, the coal content should not fall below 10 percent nor the char content exceed 90 percent by weight of the formulation. The use of some pitch as gas. hi order to obtain maximum desulfurization, the carbonized briquets were gradually raised in temperature at a rate of about 3 to 5 per minute and then held at a calcining temperature of 1800 F. for approximately 30 minutes. Thus where carbonization was accomplished at a binder is usually required, and this may vary from 5 about 5 to 15 percent by weight of the total formulation. ll E, approximately 4 hours was required to raise Step 2Sh0ck-heatz'ng and h0z'ding.Afier the brithe briquets from this temperature a calcining temperaquets have been prepared, they are passed to a shockture of 1800 F. heating and holding Zone, which treatment is essential for The unique nature of the desulfurization obtainable in imparting the desired strength to these briquets. This 10 the practice of the second aspect of this invention is shock-heating and holding treatment is described in the strikingly illustrated by comparison with the conventioncopending application of R. l. Friedrich et al., Serial al results obtained (Table II) when coal-char briquets No. 63 5,277, filed lanuary 22, 1957, now abandoned, and were heated under standard fixed-bed conditions for both assigned to the assignee of this application. In this step, the shock-heating and the calcining. The briquet feed which is schematically shown in FIGURE 8 as shock- 1 used for the runs shown in Table II consisted of a standheating and holding step 213, it is essential that the ard coal-char formulation consisting of 25 percent coal, surface of the briquets be heated to a temperature in 58.5 percent low-temperature carbonization char, 5.3 perhe range of 900 to 1250 F. as rapidly as possible, cent low-temperature carbonization pitch, 6.2 percent virtually instantaneously. This step, referred to as shockhigh-temperature pitch and 5.0 percent recycle coke. The heating, has been found essential to impart the esired 20 same fixed-bed coking conditions were used for all bristrength to the subsequently produced formcokc. After quets tested. They were shock-heated to a temperature of the shock-heating, the surface is maintained at a tem- 1l00 E, held at this temperature for 45 minutes, raised perature of 900 to 1250 F. until the briquets throughto a temperature of 1700" F. at a rate of 10 F. per minout have attained this temperature. The residence time of ute, and then held at 1700" F. for one-half hour. The the briquets may be varied from about minutes to 2 results for three different types of coal evaluated are hours, with a residence time of to 60 minutes usually shown Table II. sufficient. A shock-heating temperature of 1000 F, followed by holding at this temperature for a period of 45 minutes is preferred for obtaining formcoke having maxi- TABLE H mum physical strength as determined by tumbler index 30 measurement. If the residence time is too short, further treatment will subsequently introduce severe cracks and 0051 Montour Mounds- Arkwright partially fissures into the briquets resulting in a shattered product. ten ville igf g fii In general, as the dimensions of the briquets are inwright char creased, the residence time in the shock-heating and holding one hguld increasg Percent S, 151W briqucts 1.28 3.80 2.12 1.43 The heat required in the shock-heating and holding j f fff kii L10 339 L97 1445 zone may be supplied indirectly, although generally it 18 Ratio, cokfid S/raW 0-8 0- 0- 93 1.01 preferable to provide the bulk of the heat either by means of hot gases or by circulation of finely divided A11 coals used are Pittsburgh-scam, high-volatile coking bituminous heat-carrying solids, such as char particles. In its precoals ferred aspects, the steps of briquet preparation and shocka s holding generally t sr to those n is noted that the ratio of sulfur in the coked briquets scribe-:1 herein w th respect to practicing a first asp t of to that in the starting riquets is approximately that ohme Procgss of thls mventlontained in a standard by-product oven. It was also noted Step 3-Az4t0gen0us countercurrent desulfurzzmg and that when the char was preliminarily desulfmed before f 'f the bnqllets have been shockheated being incorporated into the briquets, a treatment that usuand they are trgatad m accordancg with the Second ally results in stronger product formcoke, essentially no aspect of this ifivflliion y raising them from {Empem reduction in sulfur content was obtained. bilow 13000 to a tempafatufe abovfi 1550 In Table III are shown runs performed in accordance While feeding them at almOSphaTic Pressure in a descendwith the second aspect of the process of this invention, ing column in countercurrent relation to an upwardly using an upwardly moving gas stream of only autogenous moving stream of gas comprising autogenous devolatilizadevolatilization gas at atmospheric pressure fed in contion gas. In the specific runs shown in Table III, the tinuous countercurrent relation to a descending column gas stream consisted solely of autogenous devolatilization of briquets.

TABLE III Feed Shock Heat Holding Final (3211- Tumbler SOontent SContent RatiozS Run No. Compo- Tempcr- Period clnation, Index of of Raw of Formcokc/ sition ature. F. (min) F. Product Brlqnct Formcoke Raw Coke Briquet A 1, 000 45 1, 800 88.1 3. 52 2.13 .605 A 1, 000 30 1, 850 as. 6 3. 55 2.10 .592 A 1,100 45 1,800 as. 0 3. 34 2. 09 .626 A 1, 000 45 1, 600 86. s 3. 49 2. 45 .716 A 1, 000 45 *1, s00 86. s 3. l9 2. 45 .702 B 1, 000 45 1,800 90. 4 s. 52 2.15 .611 C 1, 050 45 1,800 93. 5 1. 69 1.14 .675

*Rapid calcining: 1l001800 F. in ca. 2 hours.

Other runs: 11004800" F. in ca. 4 hours.

A: 25.0 percent Arkwright coal (2.63% S), 58.5 percent Moundsvillc low-tomperaturc-carbonization char (4.24% S), 5.3 percent lcwtcinperature-carbomzation pitch, 6.2 percent coke-oven pitch and 5.0 percent recycle coke.

B: 25.0 percent Arkwright coal, 58.5 percent Mouudsvillc l0wtcn1peraturc-carbonization char, 2.3 percent low-temperature-carbonization pitch, 9.2 percent recycle pitch and 5.0 percent recycle colzc.

C: 25.0 percent Arkwright coal, 61.5 percent partially desulfurized low-temperature Arkwright char (treated at1,350 F.) (1.45% S), 2.3 percent low-tcmperature-carbonization pitch, 0.2 percent recycle pitch, and 2.0 percent recycle coke.

As may be seen from Table 1H, substantial and significant reductions in the percentage sulfur content of the product formcose compared with the percentage sulfur content of the coal-char feed were obtained in all instances, ratios as low as 59 percent being obtained. it 's f rther si nificant to note that even where a prelhninarily partially desulfurized char was used, substantial reductions were still obtained. It was found that where a partially desulfurized char was used, a tumbler index for product coke of 93.5 percent was obtained, which corresponds to a formcolte or" substantially greater strength than one prepared from a char which had not been preliminarily desulfurized. This preliminary desulfurization is readily accomplished by treatment of the char with devolatilization gas under fluidized conditions as shown, for example, in US. Patent 2,717,868.

The autogenous devolatilization gas produced during the desulfurizing and calcining step, caculated on a nitro gen and hydrogen sulfide-free basis, had an average composition as follows:

The gases were determined chromatographically, with the exception of hydrogen. Inasmuch as the total pressure of the devolatilization gas used was substantially atmospheric, the partial pressure of the hydrogen in the gas was Well below one atmosphere.

in general, the coal-char agglomerates are preferably formed by bricuetting techniques followed by heat treatment of these briquets as previously described. However, the use of coal-char agglomerates formed by hottumbling is also contemplated as within the scope of this invention.

B. DESULFURIZATION OF HOT-TUMBLED AGGLOMERATES In a typical run for preparing hot-tumbled agglomerates, a feed was prepared consisting of equal parts by Weight of finely divided high-volatile coal and fluidize low-temperature carbonization char. These were blended together for twenty minutes in a twin-shell blender. The mixed feed was then withdrawn and placed in a kiln having a 14-inch internal diameter. The temperature was gradually raised, ten minutes being required to raise the temperature from 760 E. to 800 F., the latter temperature being the preferred carbonization temperature in that hot-tumbled agglomerates carbonized at this temperature yielded formcoke of maximal strength. A residence time of ten minutes at 800 5. Was maintained. Particles of /2-lnch by 4-inch size were obtained. The hot-tumbled agglomerates were calcined at 180il F. and yielded a formcoke having a tumbler index of 97.0. Thus the formcoke obtained from the hot-tumbled coal-char agglomerates showed a somewhat better strength than conventional high-temperature metallurgical coke.

Where hot-tumbled coal-char agglomerates are used as feed in the process of this invention, it is preferred that they be carbonized during the hot-tumbling process itself, i.e., by heating to a minimum temperature between and 960 F. The carbonized agglomerates may then be fed at atmospheric pressure directly into zone 214 for desulfurizing and calcining in a countercurrent autogenous gas stream, as described with respect to the briquets. Where the hot-tumbled agglomerates are not substantially carbonized during forming i.e., they are formed at tumbling temperatures below 890 1 then they are first fed into zone 213 for treatment therein in a similar manner to the carbonization treatment for the briquets, and are then fed to zone 214. In preparing the hot-tumbled agglomerates, a char content of about to 70 percent by weight of the coal-char blend is suitable. The

2'"? 1.1:] carbonized agglomerates, either carbonized in zone 213 by a shock-heating and holding treatment or kiln-carbonized during the hot-tumbling, may be used as a feed in hop er 216 to the retort illustrated in FlGl'JRl-E. 10. in tin-carbonized form, they may be fed to the unitary furnace illustrated in FIGURE 11.

While this invention is primarily directed to the production of low-sulfur formcoke of metallurgical grade for reducing iron ores in a blast furnace, the formc-oke produced may be used in other applications. Where a high order or" physical strength is not an essential requirement, the production of desulfurized formcoke in accordance with this process need not be carried beyond the desulfurization stage, namely at a temperature above 1500 F. Such desulfurized but not substantially calcined formccke can be used in non-ferrous metallurgy, in shallow-bed reduction, in electric furnace smelting, in phosphorus reduction furnaces or the like.

it is further recognized that various modifications may generally be made with respect to the processing of the coal-char feed in the step of agglomeration, whether by briquetting or hot-tumbling, and in the step of shockheating and holding. Several such modifications are shown in the copending applications previously referred to. However, this invention is particularly directed to a desulfurization process for blends of bituminous coal and low temperature carbonization char wherein carbonized agglomerates are desulfurized and calcined either under pressurized conditions with recycle or under atmospheric conditions when moving in continuous countercu-rrent relation to an autogenous devolatilization gas. Various combinations of these two aspects of our process may also be utilized. By the process of this invention there is not produced formcolte of acceptable metallurgical grade for use in a blast furnace utilizing coals heretofore unavailable for use as metallurgical coals. It will of course be understood that other modifications of this invention will also suggest themselves to those skilled in this art with respect to the combination of steps shown, in addition to those specifically illustrated herein. Accordingly, the scope of this invention is to be determined in accordance with the objects and claims thereof.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The method for preparing low-sulfur calcined for i coke of metallurgical grade which comprises heating coalchar agglomerates, including calring bituminous coal and low-density char obtained by a low temperature carbonization below 1400" F. of caking bituminous coal, the char content of the coal-char agglomerates being at least 40 percent by Weight thereof, at a carbonization temperature not greater than 1250" F. to carbonize the agglomerates, heating the carbonized agglomerates from a temperature below i? to a temperature above 1550" P. while feeding them at least at atmospheric pressure in a descending column in countercurrent relation to an upwardly moving stream of gas consisting principally of hydrogen, whereby desulfurization and calcining of the agglomerates are efiected, and recovering the agglomerates as low-sulfur calcined formcoke of metallurgical grade.

2. The method for preparing low sulfur calcined formcolre which comprises preparing briquets including (a) char having a low bulk density and obtained via low temperature carbonization of bituminous coal, and (b) caking bituminous coal, virtually instantaneously heating the surface of said briquets to a temperature in the range 909 to 1250" F., maintaining the surface at a temperature of 906 to 1250 F. until the briquets attain a temperature above 900 throughout, thereafter heating said briquets to a temperature above 1550 F., in the presence of a gas having a partial pressure of hydrogen greater than one atmosphere and having a volume ratio of H S/H less than 0.02, separately recovering said gas and said briquets, and recovering low sulfur calcined formcoke.

3. The method according to claim 2 wherein said briquets include (a) char having a bulk density less than about 30 pounds per cubic foot and obtained by a fluidized loW temperature carbonization of high volatile bituminous coal and (b) caking high volatile bituminous coal.

4. The method for preparing low sulfur calcined formcoke which comprises preparing briquets including (a) char having a bull: density less than about 30 pounds per cubic foot and being obtained via fluidized low temperature carbonization of high volatile coal, and (b) caking high volatile coal, virtually instantaneously heating the surface of said briquets by direct contact with a heating medium to a temperature in the range 900 to l250 F, maintaining said surface at a temperature of 900 to 1250 F. until the briquets attain a temperature above 900 throughout, thereafter heating said bn'quets to a temperature above 1550 :F., in the presence of a gas havin a partial pressure of hydrogen greater than one atmosphere and having a volume ratio of H S/H less than 0.02, and separately recovering said gas and said briquets, thereafter cooling said briquets to a temperature below about 600 F. and recovering loW sulfur calcined formcoke.

5. The method for preparing low sulfur calcined formcoke from high sulfur high volatile eaking coal which comprises subjecting a portion of said coal to low temperature carbonization under fluidized conditions to prepare a finely divided char having a bulk density less than about 30 pounds per cubic foot, mixing a portion of said char With a portion of said coal and preparing briquets from the resulting admixture, virtually instantaneously heating the surface of said briquets to a temperature in the range 900 to 1250 F, maintaining said surface at a temperature of 900 to 1250 F. until the briquets attain a temperature above 900 throughout, thereafter heating said 'briquets to a temperature above 1550 F, in the resence of a gas having a partial pressure of hydrogen greater than one atmosphere and having a volume ratio of H S/H less than 0.02, and separately recovering said gas and said briquets, thereafter cooling said briquets to a temperature below about 600 F. and recovering low sulfur calcined formcolre.

6. The method for preparing low sulfur calcined formcoke Which comprises preparing high sulfur briquets including (a) char having a bulk density less than about 30 pounds per cubic foot and being obtained via fluidized low temperature carbonization of high volatile coal, and (b) caking high volatile coal, virtually instantaneously heating the surface of said briquets to a temperature in the range 900 to 1250 F, maintaining said surface at a temperature of 900 to 1250 F. for 30 to 60 minutes unth the briquets attain a temperature above 90 throughout, thereafter heating said briquets for one to three hours to a temperature above 1550" F, in the presence of a gas having a partial pressure of hydrogen greater than one atmosphere and having a volume ratio of H S/H less than 0.02, and separately recovering said gas and said briquets, thereafter cooling said briquets to a temperature below about 600 F. and recovering low sulfur calcined formcoke.

7. The method for preparing low sulfur calcined formcoke which comprises preparing briquets including (a) char having a bulk density less than about 30 pounds per cubic foot and being obtained via fluidized low temperature carbonization of high volatile coal, and (b) caking high volatile coal, introducing said briquets into a shockheating and holding zone, introducing finely divided fluidized heat carrier medium into said shocltheating and holding zone, introducing fiuidizing gases into said shockheat-ing and holding zone to maintain said heat carrier medium under fluidizing conditions surrounding briquets confined therein to provide virtually instantaneous heating of the surface of said briquets to a temperature in the range 900 to 1250 F. and to maintain said surface at a temperature of 900 to 1250 F. until the biiquets attain a temperature above 900 throughout, recovering from said shockheating and holding zone evolved tar vapors and hydrocarbon-rich gas along with fluidizing gases, separately recovering said heat carrier for reheating thereof and separately recovering coked briquets, introducing said coked briquets into a combined desulfurizing and calcining zone and heating said briquets therein to a tem per re above 1550" E, in the presence of a gas having a partial pressure of hydrogen greater than one atmosphere and having a volume of H S/H less than 0.02, separately recovering said gas and said briqucts, thereafter cooling said briquets to a temperature below about 600 F. and recovering low sulfur calcined formcolre.

8. The method for preparing low sulfur calcined formcoke which comprises preparing briquets including (a) char having a built density less than about 30 pounds per cubic foot and being obtained via fluidized loW temperature carbonization of high volatile coal, and (b) caking high volatile coal, introducing said briquets into a shockheating and holding zone, passing hot gases into said shockheating and holding zone to provide virtually instantaneous heating of the surface of said briquets to a temperature in the range 900 to 1250" F and to maintain said surface at a temperature of 900 to 1250 until the briquets attain a temperature above 900 throughout, recovering from said shockheating and holding zone evolved tar vapors and hydrocarbon-rich gases and separately recovering coked briquets, introducing said coked briquets into a combined desulfurizing and calcining zone and heating said briquets therein to a temperature above 1550 F, in the presence of a gas having a partial press re of hydrogen meater than one atmosphere and having a volume ratio of H S/l-l less than 0.02, separately recovering said gas and said briquets, thereafter cooling said 'briquets to a temperature below about 600 F. and recovering low sulfur calcined bn'quets.

9. The method for preparing loW sulfur cflcined formcoke which comprises preparing briquets including (a) char having a bulk density less than about 30 pounds per cubic foot and being obtained via fluidized low temperature carbonization of high volatile coal, and (b) caking 'iigh' volatile coal, virtually instantaneously heating the surface of said briquets to a temperature in the range 900 to 1250 F, maintaining said surface at a temperature of 900 to 1250 F. until the briquets attain a temperature above 900 throughout, thereafter introducing said briquets into a desulfurizing and calcining zone, introducing into said desulfurizing and calcining zone a heating gas substantially free of H S and containing sufiicient hydrogen to maintain therein a partial pressure of hydrogen greater than one atmosphere at a rate of from 5 to 30 standard cubic feet of hydrogen for each pound of briquets enterin said desulfurizing and calcining zone, said heating gas having suflicient sensible heat to raise the temperature of briquets in said desulfurizing and calcining zone above F., separately recovering said gas and said briquets, thereafter cooling said briquets to a temperature below about 600 F. and recovering low sulfur calcined formcoke.

10. The method for preparing low sulfur calcined formcoke WtL'ch comprises preparing briquets including (a) char having a bulk density less than about 30 pounds per cubic foot and being obtained via fluidized low temperature carbonization of high volatile coal, and (b) caking high volatile coal, virtually instantaneously heating the surface of said briquets to a temperature in the range 900 to 1250" F., maintaining said surface at temperature of 900 to 1250 F. until the briquets attain a temperature above 900 throughout, thereafter introducing said briquets into a desulfurizing and calcining zone, introducing at a sutficient rate to heat said briquets to a temperature above 1550 F. into said desulfurizing and calcining zone finely divided fiuidizable heat carrying ma terial which is capable of reacting with hydrogen sulfide to form solid sulfides in the presence of hydrogen gas and also capable of rejecting sulfide sulfur under oxidative conditions, further introducing fiuidizing gases into said 

1. THE METHOD FOR PREPARING LOW-SULFUR CALCINED FORMCOKE OF METALLURGICAL GRADE WHICH COMPRISES HEATING COALCHAR AGGLOMERATES, INCLUDING CAKING BITUMINOUS COAL AND LOW-DENSITY CHAR OBTAINED BY A LOW TEMPERATURE CARBONIZATION BELOW 1400*F. OF CAKING BITUMINOUS COAL, THE CHAR CONTENT OF THE COAL-CHAR AGGLOMERATES BEING AT LEAST 40 PERCENT BY WEIGHT THEREOF, AT A CARBONIZATION TEMPERATURE NOT GREATER THAN 1250*F. TO CARBONIZE THE AGGLOMERATES, HEATING THE CARBONIZED AGGLOMERATES FROM A TEMPERATURE BELOW 1300*F. TO A TEMPERATURE ABOVE 1550*F. WHILE FEEDING THEM AT LEAST AT ATMOSPHERIC PRESSURE IN A DESCENDING COLUMN IN COUNTERCURRENT RELATION TO AN UPWARDLY MOVING STREAM OF GAS CONSISTING PRINCIPALLY OF HYDROGEN, WHEREBY DESULFURIZATION AND CALCINING OF THE AGGLOMERATES ARE EFFECTED, AND RECOVERING THE AGGLOMERATES AS LOW-SULFUR CALCINED FORMCOKE OF METALLURGICAL GRADE. 